Deploying an egress router pod in redirect mode - OVN-Kubernetes network plugin | Networking

Egress router custom resource
Deploying an egress router in redirect mode

As a cluster administrator, you can deploy an egress router pod to redirect traffic to specified destination IP addresses from a reserved source IP address.

The egress router implementation uses the egress router Container Network Interface (CNI) plugin.

Egress router custom resource

Define the configuration for an egress router pod in an egress router custom resource. The following YAML describes the fields for the configuration of an egress router in redirect mode:

apiVersion: network.operator.openshift.io/v1
kind: EgressRouter
metadata:
  name: <egress_router_name>
  namespace: <namespace>  (1)
spec:
  addresses: [  (2)
    {
      ip: "<egress_router>",  (3)
      gateway: "<egress_gateway>"  (4)
    }
  ]
  mode: Redirect
  redirect: {
    redirectRules: [  (5)
      {
        destinationIP: "<egress_destination>",
        port: <egress_router_port>,
        targetPort: <target_port>,  (6)
        protocol: <network_protocol>  (7)
      },
      ...
    ],
    fallbackIP: "<egress_destination>" (8)
  }

1	Optional: The `namespace` field specifies the namespace to create the egress router in. If you do not specify a value in the file or on the command line, the `default` namespace is used.
2	The `addresses` field specifies the IP addresses to configure on the secondary network interface.
3	The `ip` field specifies the reserved source IP address and netmask from the physical network that the node is on to use with egress router pod. Use CIDR notation to specify the IP address and netmask.
4	The `gateway` field specifies the IP address of the network gateway.
5	Optional: The `redirectRules` field specifies a combination of egress destination IP address, egress router port, and protocol. Incoming connections to the egress router on the specified port and protocol are routed to the destination IP address.
6	Optional: The `targetPort` field specifies the network port on the destination IP address. If this field is not specified, traffic is routed to the same network port that it arrived on.
7	The `protocol` field supports TCP, UDP, or SCTP.
8	Optional: The `fallbackIP` field specifies a destination IP address. If you do not specify any redirect rules, the egress router sends all traffic to this fallback IP address. If you specify redirect rules, any connections to network ports that are not defined in the rules are sent by the egress router to this fallback IP address. If you do not specify this field, the egress router rejects connections to network ports that are not defined in the rules.

Example egress router specification

apiVersion: network.operator.openshift.io/v1
kind: EgressRouter
metadata:
  name: egress-router-redirect
spec:
  networkInterface: {
    macvlan: {
      mode: "Bridge"
    }
  }
  addresses: [
    {
      ip: "192.168.12.99/24",
      gateway: "192.168.12.1"
    }
  ]
  mode: Redirect
  redirect: {
    redirectRules: [
      {
        destinationIP: "10.0.0.99",
        port: 80,
        protocol: UDP
      },
      {
        destinationIP: "203.0.113.26",
        port: 8080,
        targetPort: 80,
        protocol: TCP
      },
      {
        destinationIP: "203.0.113.27",
        port: 8443,
        targetPort: 443,
        protocol: TCP
      }
    ]
  }

Deploying an egress router in redirect mode

You can deploy an egress router to redirect traffic from its own reserved source IP address to one or more destination IP addresses.

After you add an egress router, the client pods that need to use the reserved source IP address must be modified to connect to the egress router rather than connecting directly to the destination IP.

Prerequisites

Install the OpenShift CLI (oc).
Log in as a user with cluster-admin privileges.

Procedure

Create an egress router definition.
To ensure that other pods can find the IP address of the egress router pod, create a service that uses the egress router, as in the following example:
```
apiVersion: v1
kind: Service
metadata:
  name: egress-1
spec:
  ports:
  - name: web-app
    protocol: TCP
    port: 8080
  type: ClusterIP
  selector:
    app: egress-router-cni (1)
```
1 Specify the label for the egress router. The value shown is added by the Cluster Network Operator and is not configurable.

After you create the service, your pods can connect to the service. The egress router pod redirects traffic to the corresponding port on the destination IP address. The connections originate from the reserved source IP address.

Verification

To verify that the Cluster Network Operator started the egress router, complete the following procedure:

View the network attachment definition that the Operator created for the egress router:
```
$ oc get network-attachment-definition egress-router-cni-nad
```
The name of the network attachment definition is not configurable.
Example output
```
NAME                    AGE
egress-router-cni-nad   18m
```

View the deployment for the egress router pod:

$ oc get deployment egress-router-cni-deployment

The name of the deployment is not configurable.

Example output

NAME                           READY   UP-TO-DATE   AVAILABLE   AGE
egress-router-cni-deployment   1/1     1            1           18m

View the status of the egress router pod:

$ oc get pods -l app=egress-router-cni

Example output

NAME                                            READY   STATUS    RESTARTS   AGE
egress-router-cni-deployment-575465c75c-qkq6m   1/1     Running   0          18m

View the logs and the routing table for the egress router pod.

Get the node name for the egress router pod:

$ POD_NODENAME=$(oc get pod -l app=egress-router-cni -o jsonpath="{.items[0].spec.nodeName}")

Enter into a debug session on the target node. This step instantiates a debug pod called <node_name>-debug:
```
$ oc debug node/$POD_NODENAME
```
Set /host as the root directory within the debug shell. The debug pod mounts the root file system of the host in /host within the pod. By changing the root directory to /host, you can run binaries from the executable paths of the host:
```
# chroot /host
```

From within the chroot environment console, display the egress router logs:

# cat /tmp/egress-router-log

Example output

2021-04-26T12:27:20Z [debug] Called CNI ADD
2021-04-26T12:27:20Z [debug] Gateway: 192.168.12.1
2021-04-26T12:27:20Z [debug] IP Source Addresses: [192.168.12.99/24]
2021-04-26T12:27:20Z [debug] IP Destinations: [80 UDP 10.0.0.99/30 8080 TCP 203.0.113.26/30 80 8443 TCP 203.0.113.27/30 443]
2021-04-26T12:27:20Z [debug] Created macvlan interface
2021-04-26T12:27:20Z [debug] Renamed macvlan to "net1"
2021-04-26T12:27:20Z [debug] Adding route to gateway 192.168.12.1 on macvlan interface
2021-04-26T12:27:20Z [debug] deleted default route {Ifindex: 3 Dst: <nil> Src: <nil> Gw: 10.128.10.1 Flags: [] Table: 254}
2021-04-26T12:27:20Z [debug] Added new default route with gateway 192.168.12.1
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat PREROUTING -i eth0 -p UDP --dport 80 -j DNAT --to-destination 10.0.0.99
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat PREROUTING -i eth0 -p TCP --dport 8080 -j DNAT --to-destination 203.0.113.26:80
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat PREROUTING -i eth0 -p TCP --dport 8443 -j DNAT --to-destination 203.0.113.27:443
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat -o net1 -j SNAT --to-source 192.168.12.99

The logging file location and logging level are not configurable when you start the egress router by creating an EgressRouter object as described in this procedure.

From within the chroot environment console, get the container ID:

# crictl ps --name egress-router-cni-pod | awk '{print $1}'

Example output

CONTAINER
bac9fae69ddb6

Determine the process ID of the container. In this example, the container ID is bac9fae69ddb6:
```
# crictl inspect -o yaml bac9fae69ddb6 | grep 'pid:' | awk '{print $2}'
```
Example output
```
68857
```
Enter the network namespace of the container:
```
# nsenter -n -t 68857
```
Display the routing table:
```
# ip route
```
In the following example output, the net1 network interface is the default route. Traffic for the cluster network uses the eth0 network interface. Traffic for the 192.168.12.0/24 network uses the net1 network interface and originates from the reserved source IP address 192.168.12.99. The pod routes all other traffic to the gateway at IP address 192.168.12.1. Routing for the service network is not shown.
Example output
```
default via 192.168.12.1 dev net1
10.128.10.0/23 dev eth0 proto kernel scope link src 10.128.10.18
192.168.12.0/24 dev net1 proto kernel scope link src 192.168.12.99
192.168.12.1 dev net1
```